Someone pointed out on the BBC News that the Malaysian plane was hit not by a 'rocket' but by a 'missile'. From the dictionary definitions I have looked up I cannot tell the difference.

MissileAn object which is forcibly propelled at a target, either by hand or from a mechanical weapon.

Rocketa cylindrical projectile that can be propelled to a great height or distance by the combustion of its contents...

Oxford Dictionary of English

Is it therefore the case that a rocket is always a missile, but that a missile is not necessarily a rocket? A cricket ball can be regarded as a missile but is clearly not a rocket. But why could the type of weapon which it is believed brought down Flight MH17 not be described as a 'rocket'?

Even modern military missiles are not necessarily rockets. Cruise missiles usually have a turbofan for propulsion. A rocket is a device that carries its own supply of energy and reaction mass. The reaction mass is what it pushes against; it doesn't push against the air. This is why a rocket can operate in the vacuum of outer space.
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Ben CrowellJul 19 '14 at 22:12

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In military lingo, a rocket is a short-range portable weapon launched from hand like the RPG; a missile is a guided long-range weapon launched from a fixed or mobile platform.
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Question OverflowJul 20 '14 at 1:25

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Etymologically, "missile" means something sent. It's derived from "mittere," which means to send or let go. Cf. "missive." When you shoot an arrow at a target, you let the arrow go and send it to the target.
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Ben CrowellJul 20 '14 at 14:40

A missile is generally understood to be a weapon. A rocket need not be - consider the various rockets used to launch satellites and astronauts into space.
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user2310967lessJul 20 '14 at 14:46

A cricket ball as bowled is a missile, in that the bowler's intent is to damage the current arrangement of the wicket. As hit by the batsman, not so much. A baseball as pitched is not a missile unless it is pitched as an intentional bean-ball, among the foulest of fouls in that game.
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Brian DonovanJul 20 '14 at 19:00

6 Answers
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A rocket is so called on the basis of its mode of self-propulsion. A missile is so called on the basis of its being propelled, by a rocket engine or otherwise, for the purpose of doing damage, as a weapon. The two categories overlap considerably, since rockets are commonly used as propulsion for missiles, with or without in-flight guidance systems. Put an explosive warhead on top of an Atlas rocket, and launch it at an enemy (or practice target), the whole assembly becomes a missile. Put a Mercury capsule on top with John Glenn inside, it is a rocket but not a missile. The weapon that reportedly brought down the Malaysian airliner was (or is, if considered generically) both a rocket and a missile, and can properly be termed either one—though without the explosive payload that transforms it from mere rocket to missile it would probably not have brought the plane down, so missile is the more adequate term in this case.

I am wondering how this connects to @Ben Crowell's comment above. He maintains that anything which is 'sent' is a missile.
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WS2Jul 20 '14 at 16:52

@WS2: A letter may be sent, but it is a missive, not a missile. Same root, but distinctly different derivative; and the purpose of harm differentiates the meanings. OED s.v. missile 2.a.: "An object propelled (either by hand or mechanically) as a weapon at a target" (emphasis added).
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Brian DonovanJul 20 '14 at 18:02

Now would that make the Latin master's blackboard duster a missile? It seems, from what you say, to depend on the intent with which it was thrown. Was it a weapon intended to harm the person on the receiving end, or simply to wake them up so that they paid attention to what they were being taught?
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WS2Jul 20 '14 at 19:21

@WS2, I think the intent is somewhat hostile, to cause a modicum of physical pain, and respiratory distress, and embarrassment--so yes, missile. It is a distinctly aggressive act on the part a teacher.
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Brian DonovanJul 20 '14 at 19:24

Nowadays he would probably have been locked up.
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WS2Jul 20 '14 at 19:29

But when my Latin master, sixty years ago, used to throw the blackboard duster at me, that was a 'missile' wasn't it? Seems like we have to acknowledge different meanings of 'missile'.
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WS2Jul 20 '14 at 7:14

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Well, yes, but you weren't asking what a missile was in general, you were asking why the weapon used to bring down MH17 was called a missile and not a rocket.
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ElendilTheTallJul 20 '14 at 7:39

@Ws2 - yes and is still used in police/news reports. "Youths hurled missiles at police" doesn't mean that they were tossing Tridents like cabers.
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mgbJul 20 '14 at 18:17

Summary: a rocket is a means of propulsion; a missile is something that is propelled (possibly by a rocket).

A rocket is an engine that propels an object by combustion, where both the both the propellant and oxidizer are contained in the engine, as opposed to being input from outside (e.g., the oxygen does not come from the surrounding air or water).

A missile is any object that is propelled (typically in 3 dimensions, as through space, air, or water).

Some missiles are propelled by an exterior force, and after that initial push are simply ballistic: falling. Others have an on-board engine: they are self-propelled. A combination would be essentially just falling but with one or more small engines on board that can change the trajectory slightly.

Of the latter (missiles with on-board engines), some have self-contained engines; others can make use of oxygen in the fluid they pass through. Of those that have engines, the best known have rocket engines.

+1 but I don't see how an object could be propelled in fewer than three dimensions, given the structure of the universe we live in! In particular, a ball rolled across the floor is not a missile.
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David RicherbyJul 20 '14 at 9:20

@DavidRicherby To my mind at least, a ball rolling across the floor can be a missile. And even a cannonball moving through space ballistically might well have a plane (2D) trajectory. Anyway...
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DrewJul 20 '14 at 17:44

Rocket's carry both their propellant and oxidizer, and are usually unguided - their trajectory is determined and fixed at launch time, however they may have the capacity for small course corrections. They are not capable of completely changing trajectory or assuming a guided path, that would make them a (guided) missile.

However, it is not that cut and dry. ICBM (inter-continental ballistic missiles) fit the definition of a rocket - they follow a fairly set trajectory after some initial guidance, with only the capacity to make small course corrections. And it would not be in any way out of the ordinary to refer to such a thing as a "rocket". However the official name is missile.

It is absolutely true that the term "missile" can refer to any propelled object, and historically was so. So sling shots, catapult rounds, even arrows, could all technically be called missiles. However, the common usage meaning of "missile" today is a guided military weapon system that has the capacity to assume a non-kinetic guided trajectory, change course, and possibly lock onto and follow targets. Ground to air missiles and air-to-air missiles usually carry both their fuel and oxidizer, giving them something in common to rockets (although are never referred to as such), whereas air-to-ground missiles usually have air-breathing jet engines, and are often referred to as "cruise missiles", because they can cruise for long distances while following a controlled, guided path.

Back to the ICBM example - rockets are usually BIG. So if a "missile" was large enough, and did not have an air-breathing engine, it would probably be referred to as a rocket even if it was highly controlled and guided.

Missiles are almost exclusively military - humans will always be taking rockets to the Moon and maybe even Mars, never a missile ;-)

It can be a particular kind of military weapon, but it can be any object that is thrown with the intention of causing injury or damage.

In the context of the question, which is the Malaysian airliner that crashed in Ukraine, the particular, military meaning applies. The introduction of the article at the following link http://en.wikipedia.org/wiki/Missile , states "In a modern military usage, a missile, or guided missile, is a self-propelled guided weapon system, as opposed to an unguided self-propelled munition, referred to as just a rocket."

In other words, in a military context, a rocket is an unguided, rocket-powered weapon, with no steering ability. A missile is a self-propelled weapon, often rocket-powered (but not always), that has some kind of guidance system so that it can steer in flight, towards its target.

That would be why someone pointed out on BBC News that the Malaysian plane was hit not by a 'rocket' but by a 'missile'. It is very unlikely that an unguided rocket fired from land, which requires a direct hit on its target, to explode, would be able to hit an aircraft in flight, especially one flying as high as that airliner was reported to be. Potential attackers would have to use a missile, which can steer towards its target and would have a proximity fuse http://en.wikipedia.org/wiki/Proximity_fuze , which means that it would not require a direct hit on its target, to explode.

I don't think "missile" has become restricted to something self-propelled and guided. That's one type of missile, but it's still correct to refer to a thrown rock as a missile.
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Ben CrowellJul 19 '14 at 22:03

@placeholder: It is, and it isn't. The technical definition of jet engine certainly does include rocket engines; but the everyday understanding of the term does not.
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ruakhJul 20 '14 at 1:32

Actually, this is correct. By the terms that I am familiar with: Reaction engines (propulsion by means of forced expulsion), of which jet engines are a subtype (high speed jet of fluid), of which rockets are a subtype (only propellent mass, i.e. no external air, used to form the jet).
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dotancohenJul 21 '14 at 6:04